Motors are used as equipment for driving that coverts electrical energy into mechanical energy for industrial use in the field of household appliances, the field of automobiles, and the like. In JP-A-2002-359938 (FIG. 9), for example, there is disclosed a slot type three-phase brushless motor because of its inexpensive structure, the simplicity of its drive circuit, and the like. There are various types of motors, single-phase, two-phase, and three-phase, and different types are used depending on applications. Especially, three-phase motors are excellent in controllability and can be connected in Δ formation and in Y formation. Therefore, they have an advantage that they can be driven in normal and reverse rotations by a smaller number of transistor elements.
In JP-A-7-227075 (FIG. 2), there is disclosed a claw teeth type motor whose stator is constructed of an annular core provided with plural claw poles and an annular coil provided inside this annular core.
In the claw teeth type motor in JP-A-7-227075 (FIG. 2 ), the material of its stator core is formed of SPCC (cold-rolled steel plate: Japanese Industrial Standard) or the like. An annular coil is clamped between annular core portions and claw poles (claw poles) are formed on the inner circumferential area by bending.
However, this claw teeth type motor involves problems. The SPCC is inferior in magnetic characteristic and, in bent portions on which magnetic flux is concentrated, the magnetic characteristic is further degraded because of stress strain due to the production of residual stress. For this reason, a large iron loss is produced in the core of this motor. Since SPCC is bent, residual stress is produced in bent portions in the core and stress strain incurs further degradation in magnetic characteristic. Especially, since magnetic flux is concentrated on these bent portions, a large iron loss is produced there. That is, the claw teeth type motor using SPCC, disclosed in JP-A-7-227075 (FIG. 2), is very inefficient.
To avoid degradation in magnetic characteristic due to bending of a core, a powder core obtained by compacting insulatively coated iron powder can be used. However, stator cores using a powder core involve a problem of low mechanical strength. For example, a powder core compact are 10 MPa in bending strength, which is lower than that of iron plates and the like, and are also susceptible to impact. When a motor is constructed, consequently, it must be so structured that it can withstand torque reaction force produced between a stator and a rotor, external impact, disturbances, such as vibration, and the like.
Consequently, it is an object of the invention to provide a claw teeth type electric rotary machine in which the mechanical strength of a stator can be enhanced and a manufacturing method for stators.